The present invention relates generally to an apparatus for monitoring a rotor mounted by bearings within a stationary housing and, more particularly, to such an apparatus which provides an indication of radial and axial wear of the bearings and provides an indication of whether the rotor is rotating and, if so, its direction and speed of rotation. While the present invention is generally applicable to rotary machines, it is particularly applicable to sealless rotor pumps and accordingly will be described herein with reference to this application.
Sealless rotor pumps are known in the prior art and are commonly used in the nuclear and chemical fields. Such pumps normally include a rotor having a shaft mounted for rotation by bearings within a stationary housing. A containment shell is provided within the housing for enclosing the rotor and forming a portion of a sealed chamber through which fluid passes as it is circulated by the pump. The bearings and the rotor shaft are contained within the containment shell and are immersed in the fluid being pumped, which is often of a corrosive nature. As a result, the rotor shaft and/or the bearings may wear rapidly, making it difficult to predict when the bearings and/or the shaft must be replaced. If excessive bearing or shaft wear occurs and is not repaired, the containment shell may be damaged by the rotor risking rupture of the shell and leakage of fluid from the pump.
Numerous devices have been proposed to provide a warning of bearing or shaft wear. For example, in U.S. Pat. No. 4,924,180 a detection device is disclosed which serves to measure bearing or shaft wear in a pump. The device includes a plurality of magnets which are positioned about the outer circumference of the rotating shaft of the pump. Surrounding the rotating shaft is a stationary collar which houses at least two coils. The two coils are positioned substantially diametrically opposite to one another and sense magnetic flux density as the shaft rotates to generate first and second voltage signals. A differential amplifier is provided which compares the first and second voltage signals to one another to generate a third signal. The third signal is then compared to a reference signal which is proportional to shaft speed to obtain a compensated third signal representative of shaft or bearing wear.
A limitation of the device disclosed in the referenced patent is that the flux density sensors, i.e., the coils, are not capable of generating flux density signals which are independent of shaft speed. Consequently, a reference signal must be generated to compensate for the effect of shaft speed before a signal can be obtained which is representative of shaft or bearing wear. Furthermore, the device is not capable of monitoring axial bearing wear, the direction of rotation of the shaft, the amount of electrical power driving the pump, and temperatures within the pump.
Accordingly, there is a need for an improved monitoring device for a sealless pump which is capable of monitoring shaft or bearing wear independent of shaft speed. Preferably, such an improved monitoring device would also be capable of monitoring axial bearing wear, whether the shaft is rotating, and if so, the direction and speed of rotation of the shaft, the amount of electrical power driving the pump, and at least one temperature within the pump, all to the end of improving performance and reliability of the sealless pump.